Detecting emissions from valve packing

ABSTRACT

A sensor configured to measure rate of flow of fugitive emissions on a flow control. The configurations may include devices that are sensitive to low flow or low pressure. These devices may include piezo-electric films or foams. These materials may deflect in response to flow of fluid along the outer surface of the reciprocating shaft. In one implementation, the embodiments can generate average leak rate over time and measure against regulation or specifications to ensure appropriate operation (e.g., leak suppression) of the flow control. Storing this data can provide a database of information that allows operators to benchmark performance of the flow control, for example, to correlate leaks to a certain date or time. This feature may, in turn, permit the operators to also correlate the device-specific performance to overall plant or network operations.

BACKGROUND

Flow controls operate in myriad applications. Many find use inindustrial facilities, including as part of process lines. Designs forthese devices are meant to accurately regulate flow to meet processparameters. In some applications, like those that transport hydrocarbonsor fossil fuels, performance of the flow control is subject tosignificant regulation or operating parameters to satisfy contractor,purchasers, or end users, including allowable amounts of emissions thatmay emanate from the device. These “fugitive emissions” are oftendifficult to detect because it appears in such small quantities oroccurs on the device in areas that are difficult to reach to gatheraccurate measurements. Techniques to detect fugitive emissions may usechemical “sniffers,” thermal scanners, or acoustic or ultrasonicmodalities, all of which have their own limitations, whether due tocost, labor, accuracy, or otherwise.

SUMMARY

The subject matter of this disclosure relates to improvements to detectfugitive emissions on flow controls. Of particular interest areembodiments that can measure flow of these emissions directly on thedevice. These embodiments may utilize sensors that are sensitive to verylow flow of material that is consistent with fugitive emissions from,for example, packing material, bearings, or parts or components that mayform routes for material to escape from inside the device.

DRAWINGS

Reference is now made briefly to the accompanying drawings, in which:

FIG. 1 depicts a schematic diagram of an exemplary embodiment of anemissions sensor;

FIG. 2 depicts an elevation view of the cross-section of exemplarystructure for the emissions sensor of FIG. 1 ;

FIG. 3 depicts an elevation view of the cross-section of exemplarystructure for the emission sensor of FIG. 1 ; and

FIG. 4 depicts an elevation view of the cross-section of exemplarystructure for a flow control.

Where applicable, like reference characters designate identical orcorresponding components and units throughout the several views, whichare not to scale unless otherwise indicated. The embodiments disclosedherein may include elements that appear in one or more of the severalviews or in combinations of the several views. Moreover, methods areexemplary only and may be modified by, for example, reordering, adding,removing, and/or altering the individual stages.

The drawings and any description herein use examples to disclose theinvention. These examples include the best mode and enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Anelement or function recited in the singular and proceeded with the word“a” or “an” should be understood as not excluding plural of saidelements or functions, unless such exclusion is explicitly recited.References to “one embodiment” or “one implementation” should not beinterpreted as excluding the existence of additional embodiments orimplementations that also incorporate the recited features.

DESCRIPTION

The discussion now turns to describe features of the embodiments shownin drawings noted above. As discussed, fugitive emissions from flowcontrols in place along process piping or pipelines is often regulatedto very low levels, if not wholly disallowed all together. Theembodiments herein detect onset of these emissions from parts of flowcontrols that allow for relative movement of components, for example,reciprocating or rotating movement of a shaft. These components mayinclude “packing” that forms a tight, “flow-preventing” fit. Thispacking is meant to eliminate leak paths, for example, around the outerdiameter of the shaft and between the outer diameter of the packing andthe inner diameter of the valve body. The embodiments can install on theflow control in proximity to this packing to detect minute pressuredifferences that indicate flow of material. Other embodiments are withinthe scope and spirit of this disclosure.

FIG. 1 depicts a schematic diagram of an exemplary embodiment of anemission sensor 100. This embodiment is part of a valve assembly 102,shown here with a controller 104 that has a processing unit, forexample, a processor 106 and memory 108 with executable instructions 110stored thereon. The controller 104 may couple with an actuator 112 thatconnects to a valve 114 via a valve stem 116. The valve assembly 102 mayalso include a packing unit 118 that receives the valve stem 116. Asalso shown, the emissions sensor 100 may include a sensor 120 thatcouples with the packing unit 118. The sensor 120 may generate a signalSi for use at the processing unit.

Broadly, the emissions sensor 100 is configured to measure fugitiveemissions. These configurations may include devices that can quantifyflow of material, like hydrocarbon gasses. These devices may generate aresponse to very small changes in pressure. This response, in turn, maycorrespond with very low flow of fugitive emissions.

The valve assembly 102 may be configured for use in systems thattransport materials. These configurations may connect in-line withconduit, like pipes and pipelines, as part of a process line or linesthat transfer fluids (including liquids and gasses). Hydrocarbonoperations are known to leverage these devices to regulate flow of oil &natural gas (including liquefied natural gas or “LNG”) from points ofextraction to process facilities or within the process facilitiesthemselves.

The controller 104 may be configured to exchange and process signals.These configurations may connect to a control network (or “distributedcontrol system” or “DCS”), which maintains operation of all devices onprocess lines. These operations may ensure that materials flow throughthe valve in accordance with parameters for a process. The DCS maygenerate control signals that describe or define operation of the valveassembly 102 for this purpose. For example, the control signal maydefine a commanded position for the valve assembly 102. The processingunit 106, 108, 110 may process the control signals to generate a signalto the actuator 112 that depends in large part on this commandedposition.

The actuator 112 may be configured to generate a load that works againstpressure of material. These configurations may employ pneumatic devices,although electrical or electronic devices (e.g., motors) may work aswell. For pneumatic devices, the controller 104 may deliver its signalas gas, or “instrument air.” The pneumatic devices may have a diaphragmand spring that are inside of a housing. The instrument air signalchanges pressure or load against the diaphragm inside of the housing ofthe actuator 112.

The valve 114 may be configured to fix parameters of flow into theprocess line. These configurations often include hardware that coupleswith the pipes or pipeline. Manufacture of this hardware often comportswith properties of the materials, including its composition or “phase,”for example, solid, fluid, or solid-fluid mix. The valve stem 116 mayembody an elongate, metal shaft with one end coupled to the actuator 112and its other end coupled to a closure member on the valve 114. Thisclosure member may embody a plug, ball, butterfly valve, or likeimplement that can contact with a seat to prevent flow. Location of theclosure member relative to the seat permits more or less flow ofmaterial to pass through the valve 114 to satisfy the processparameters.

The packing unit 118 may be configured to prevent flow of fluid. Theseconfigurations may include devices that form a seal with the peripheryof a shaft, like the valve stem 116. This seal can accommodate movementof the shaft. For example, the shaft may translate axially through thedevice. This type of reciprocating movement is consistent withlinear-displacement valves, where the plug (or closure member) travelsvertically relative to the seat. In other implementations, the shaft mayrotate in the device. Rotary movement is often found in butterfly-valvesthat accommodate flow perpendicular to the axis of rotation.

The sensor 120 may be configured to measure parameters that indicateflow of material. These configurations may include devices that aresensitive to small changes in pressure. These devices may embodypiezo-electric sensors with films or foams that deflect in response tosmall forces, like those that might result due to flow of fugitiveemissions. The sensor may, in turn, generate the signal Si with a valuethat corresponds to the deflection. In one implementation, processing ofthe signal Si (at the controller 104 or processing unit, generally) mayidentify flow of material through the seal. These processes maycalculate values for a flow rate Q that is indicative of fugitiveemissions. For example, these values may correspond with Equation (1)below:

$\begin{matrix}{{Q = {\frac{\pi}{8\mu}{\left( {- \frac{dp}{dx}} \right)\left\lbrack {a^{4} - b^{4} - \frac{\left( {a^{2} - b^{2}} \right)}{\ln a/b}} \right\rbrack}}},} & {{Equation}(1)}\end{matrix}$

where Q is flow rate, μ is absolute viscosity, dp/dx is the rate ofchange of pressure in the direction of flow, and a and b are radialdimensions of an annulus through which the fugitive emissions flow.

FIG. 2 depicts an elevation view of exemplary structure for the emissionsensor 100 of FIG. 1 . The sensor 120 may include a piezo-electricsensing element 122, shown here as a thin film that wraps around orcircumscribes the valve stem 116. In one example, the thin film mayreside in a packing follower 124, for example, in a groove 126 (or“detent”). The groove 126 creates a small annular space between theinner diameter of the packing follower 124 and the valve stem 116. Avent passage 128 may extend from the groove 126 to an outer surface ofthe packing follower 124. The vent passage 128 may expose an outer partof the thin film to atmosphere. On one side, the packing follower 124 isadjacent packing material 130. A cap 132 contacts the packing follower126 on the other side. Fasteners F may secure the cap 132 to an upperpart of bonnet 134 of the valve 114. The bonnet 134 may have a bore 136to receive the follower 126, material 130, and a bushing 138. Tighteningthe fasteners F compresses the packing material 130 against the bushing138. Over time, though, flow F of fugitive emissions may develop betweenthe outer diameter of the valve stem 116 and the inner diameter of thepacking material 130. This leak may create a small pressure differentialacross the thin film as between the inner side proximate the leak andthe vented side that the vent passage 128 exposes to atmosphere. Thesmall pressure differential deflects the thin film, which generates thesignal Si. The processing unit can process this signal, as noted above,to identify flow or “leak” rate Q or other parameters that can quantifyfugitive emissions from the device.

FIG. 3 depicts a schematic diagram of an exemplary structure for theemission sensor 100 of FIG. 1 . This example has a “remote” sensingdevice 140 that houses the thin film. A flow passage 142 may connect thethin film with flow of fugitive emissions from the packing unit 118. Inone implementation, the flow passage 142 may include a conduit 144, likea plastic tube, that connects to a port 146 on the follower 124. Theport 146 may connect to a passage 148 that terminates at an opening 150proximate an interface between the follower 124 and the packing material130. The interface is shown here at the “top” of the packing material130. This configuration can direct flow of fugitive emissions to thesensing device 140. The flow may impinge on the thin film, which caninduce pressure differential and, in turn, generate the signal Si, evenat the very low flow rates consistent with “leaking” emissionsconsistent with the valve assembly 102.

FIG. 4 depicts an elevation view of the cross-section of exemplarystructure for the valve assembly 102 of FIG. 1 . The bonnet 134 maycouple with a valve body 152, typically a cast or machined metal member.The valve body 152 may have an interior cavity 154 that forms a flowpath between open ends 156. Flanges 158 at the open ends 156 can connectto adjacent conduit, like pipes or pipeline. These connections allowmaterial to flow into (and out of) the valve body 152. The flow may passthrough a trim assembly 160 that may reside in the interior cavity 154.The trim assembly 160 may include a cage 162 that houses a closuremember 164. A seat 166 may reside just below the cage 162. In use, thevalve stem 116 may couple the actuator 112 (FIG. 1 ) with the closuremember 160. The actuator 112 (FIG. 1 ) may control the position of theclosure member 164 relative to a seat 166 to regulate flow of materialthrough the trim assembly 160.

In view of the foregoing, the improvements herein are useful to manageoperation of flow controls. The embodiments outfit these devices todetect flow of fluid through certain interfaces slowly, over longperiods of time. The piezo-electric sensors, for example, are sensitiveto very low flow or very low pressure flows, which are characteristicsof fugitive emissions from the packing-valve stem interface. Thesefugitive emissions may indicate that the packing material is in need ofservice.

The examples below include certain elements or clauses one or more ofwhich may be combined with other elements and clauses to describeembodiments contemplated within the scope and spirit of this disclosure.The scope may include and contemplate other examples that occur to thoseskilled in the art. Such other examples are intended to be within thescope of the claims if they have structural elements that do not differfrom the literal language of the claims, or if they include equivalentstructural elements with insubstantial differences from the literallanguage of the claims.

What is claimed is:
 1. A flow control, comprising: a shaft having anelongate body with an outer surface; a piezo-electric sensor coupledwith the outer surface of the shaft to detect flow of fluid along theouter surface of the shaft.
 2. The flow control of claim 1, furthercomprising: packing material disposed about the outer surface of theshaft, wherein the piezo-electric sensor is in proximity to the packingmaterial.
 3. The flow control of claim 1, further comprising: packingmaterial disposed about the outer surface of the shaft, wherein thepiezo-electric sensor is in proximity to the top of the packingmaterial.
 4. The flow control of claim 1, further comprising: packingmaterial disposed about the outer surface of the shaft; and a followerinsertable onto the shaft, wherein the piezo-electric sensor coupleswith the follower.
 5. The flow control of claim 1, further comprising:packing material disposed about the outer surface of the shaft; and afollower insertable onto the shaft, the follower having a groovedisposed on its inner surface proximate the shaft, wherein thepiezo-electric sensor is disposed in the groove.
 6. The flow control ofclaim 1, further comprising: packing material disposed about the outersurface of the shaft; and a follower insertable onto the shaft with anend in proximity to the packing material wherein the piezo-electricsensor couples with the end of follower.
 7. The flow control of claim 1,further comprising: a processing unit coupled with the piezo-electricsensor, wherein the processing unit is operative to process a signalfrom the piezo-electric sensor to quantify flow of fluid.
 8. The flowcontrol of claim 1, further comprising: a processing unit coupled withthe piezo-electric sensor, wherein the processing unit is operative toprocess a signal from the piezo-electric sensor to generate a flow rateof the flow of fluid.
 9. The flow control of claim 1, wherein thepiezo-electric sensor comprises a thin film of material.
 10. The flowcontrol of claim 1, wherein the piezo-electric sensor is configured todeflect in response to the flow of fluid.
 11. A flow control,comprising: an actuator; a shaft coupled with the actuator; packingmaterial circumscribing the shaft; a thin, piezo-electric film disposedin proximity to the packing material and forming an annular ring aroundthe shaft.
 12. The flow control of claim 11, further comprising: afollower having a bore to receive the shaft, wherein the thin,piezo-electric film is disposed on an inner surface of the follower thatis in proximity to the shatf.
 13. The flow control of claim 11, furthercomprising: a follower having a bore to receive the shaft and an annulargroove that is proximate the packing material, wherein the thin,piezo-electric film is disposed in the annular groove.
 14. The flowcontrol of claim 11, further comprising: a follower slidable onto theshaft, the follower having a groove on its interior surface and a ventpassage that extends from the annular groove to its outside surface,wherein the thin, piezo-electric film is disposed in the annular groove.15. The flow control of claim 11, further comprising: a followerslidable onto the shaft, the follower having a passage that extends froman opening proximate the packing material and the shaft to a port on anoutside surface.
 16. A system, comprising: a flow control having packingmaterial disposed about a moveable shaft; and a sensor coupled with aninterface between the moveable shaft and the packing material, whereinthe sensor is configured to react to pressure differential that resultsfrom flow of fluid at the interface.
 17. The system of claim 16, furthercomprising: a processing unit coupled with the sensor, the processingunit operative to process a signal from the sensor to generate a valuefor flow rate of the flow of fluid.
 18. The system of claim 16, whereinthe sensor is configured to deflect in response to the flow of fluid.19. The system of claim 16, wherein the sensor comprises apiezo-electric film.
 20. The system of claim 16, further comprising: aconduit coupling the sensor with the interface.